The present invention relates to a conductive coating composition comprising a graphite intercalation compound and a process for preparing the graphite intercalation compound.
A conductive coating composition known in the art comprises a fine powder having in itself electrical conductivity, e.g., metals such as silver, copper and nickel, or graphite and carbon black, dispersed in various binders and solvents.
When the metallic fine powder is used, an electrical conductivity of about 10.sup.-5 .OMEGA..cm in terms of volume specific resistance is obtained. However, silver is not only remarkably high in the price per unit weight of the composition but also undergoes a great change in the price. The powder of the other metals brings about a chemical change, such as oxidation, and further no sufficient measure has been taken against the occurrence of a migration phenomenon wherein the fine metallic powder migrates between adjacent coating films.
Although a coating composition containing carbon black dispersed therein brings about no problem accompanying the use of the fine metallic powder, the electrical conductivity is not very high and 10.sup.-2 .OMEGA..cm at the highest.
It is known that a conductive coating composition prepared by graft polymerizing various monomers in a solvent and dispersing carbon black therein is mixed with a silver dispersion coating composition for the purpose of preventing the migration of silver in a coating composition containing silver dispersed therein. However, this expedient is disadvantageous in that the conductive coating composition is poor in the compatibility with the silver dispersion coating composition.
On the other hand, as is known, a graphite intercalation compound (hereinafter abbreviated to "GIC") comprises graphite and various metals or compounds intercalated between crystalline layers of the graphite.
Known metals which are intercalated into graphite include alkali metals such as Li, Na, and K and known compounds which are intercalated into graphite include metal halides such as SbF.sub.5, CuCl.sub.2, NiCl.sub.2, and FeCl.sub.2 and acid compounds such as HNO.sub.3 and H.sub.2 SO.sub.4. The above-described GIC has attracted attention as a substitute for metals because it has excellent electrical conductivity, and various processes for preparing GIC are known. For example, GIC wherein a metal chloride is intercalated is prepared by the following process (a) or (b).
(a) A process in which a mixture of an anhydrous metal chloride with graphite or a mixture of a molten salt of a metal chloride with graphite is heated in vacuo, in an inert gas or in a chlorine gas atmosphere. In this process, a reaction is usually conducted by putting a mixture of the starting materials in a glass tube or putting graphite and metal chloride at different positions in a glass tube, melt-sealing or sealing the glass tube, and heating the glass tube at 400.degree. to 500.degree. C. to react the starting materials.
(b) A process in which a mixture of graphite with a metal chloride is heated in a chlorine gas stream.
Since process (a) uses a melt-sealed or sealed glass tube or vessel, it is unsuitable for production of GIC on a commercial scale. Specifically, there is no vessel material suitable for heating a metal chloride at 400.degree. C. or above except for glass. Furthermore, although depending upon the kind of metal chlorides used, a considerable internal pressure builds up at such a high temperature due to the vapor pressure of a metal chloride itself and a chlorine gas generated by thermal dissociation of the chloride, so that it is very difficult to use a glass vessel having a large opening in a sealed state.
Further, in process (a), the reaction rate is low and the reaction time is as long as at least a day, which also makes it difficult to prepare GIC on a commercial scale.
In the case of process (b) as well, the reaction rate is low, and it takes several to ten days or longer to prepare GIC containing an intended amount of a metal, a compound, or the like intercalated between crystalline layers thereof.